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After Colburn Analogy between heat and mass transfer, the heat transfer coefficient can be determined by the mass transfer coefficient for forced or free convection.The average vapor transfer coefficients (Df) over a flat elliptic plate of naphthalene in the forced flow parallel to the minor axis are given by the following equations:for the laminar boundary layer, Df=0.737·Re2a1/2·Sc1/3dN/2aand for the turbulent, Df=0.0380·Re2a4/5·Sc1/3dN/2awhere Re2a=Reynolds number, Sc=Schmidt number, dN=melecular diffusion coefficient of naphthalene vapor into air, and 2a=length of minor axis.For the free convection in the laminar range, the average coefficients on the upper surface of a horizontal elliptic plate are given as follows: for a warm plate, Dn1=0.45(Gr·Sc)1/4dN/1and for a cold plate, Dn2=0.27(Gr·Sc)1/4dN/1where Gr and 1 are the Grashof number and the mean length of major and minor axes.For obtaining the heat transfer coefficient (hf or hn) from the corresponding mass transfer one, it is necessary to use conversion factors.The conversion take the following forms:for the forced convection, hf/Df=(ρa·cp)1/3(ka/dN)2/3and for the free convection, hn/Dn=hn1/Dn1=hn2/Dn2=(ρa·cp)1/4(ka/DN)3/4, where ρa=density, cp=specific heat, ka=thermal conductivity of air.These factors should be calculated when the reference temperatures are known.On a small elliptic plate like a citrus leaf, it is obliged to recognize the edge effect increasing the heat and mass transfer in comparison with their theoretical values. This effect may be expressed by a corrective factor (αf), that is the ratio of the observed to the theoreticl value of the average transfer coefficient.In this experiment, the transfer rates of naphthalene vapor into the air from a flate lliptic plate, whose major and minor axes are and cm respectively, were mesaured in the range of wind velocity from 5 to 500cm/sec.As the result, the observed values of the average vapor transfer coefficients are proportional to one-half power of wind velocity in the laminar flow and to the four-fifths power in the turbulent, as shown in Figs. 1 and 2.Then, the heat transfer coefficients are calculated from these values using the conversion factor, and compared with the values on a citrus leaf reported in previous in vestigation of “Leaf Temperature” (1962 and '63). The values calculated from the naphthalene vapor transfer are in good agreement with the values for the citrus leaf.Moreover, it is found the corrective factors (αf)N for the naphthalene vapor are almostly constant, independent of wind velocity. The mean values of (αf)N are 1.29 in the laminar flow and 1.36 in the turbulent.These values are nearly equal to the previously given values of αf for the heat transfer coefficients over a citrus leaf.From these results, it may be proved that the corrective factor (αf) is mainly due to theedge effect.

A Contribution to the Determination of Heat-Transfer Coefficients on a Leaf by Naphthalene Vapor Transfer